Aircraft observations of boundary layer turbulence:
Intermittency and the cascade of energy and passive scalar variance
We analyze boundary-layer velocity and temperature measurements
acquired by aircraft at 22 Hz. The calculated longitudinal velocity
third-order structure function yields approximate agreement with
Kolmogorov's four-fifths law for the scale range ~ 10-100 m with a
downscale energy flux of ~ 4 x 10-5
m2/s3. For scales greater than ~ 10 km the sign
is reversed, implying an inverse energy cascade with an estimated flux
of ~ 10-5 m2/s3 associated with 2D
stratified turbulence. The mixed structure function of longitudinal
velocity and squared temperature increment follows Yaglom's
four-thirds law in the same scale range, yielding an estimated
downscale temperature variance flux of ~ 5 x 10-7
K2/s. Analysis of higher-order structure functions yields
anomalous scaling for both velocity and temperature. The scaling also
reveals second-order multifractal phase transitions for both velocity
and temperature data. Above the transition moments, asymptotes
varying with the number of realizations argue against the log-Poisson
model. The log-Lévy model is better able to explain the
observed characteristics.
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